1) Don't spam...
2) Sometimes using multiple transformation spells over each other causes this when it runs out.
3) Make sure that the unit refrences are correct. I don't know if it makes a difference...
4) Well, check to make sure everything is right.
I would look at it for you... But it's a bad view from here... Some things in the object editor causes things to crash because of stupid reasons. If I remember correct, you can't put sounds (or was it just looping sounds... Or the regular sounds...) Either way... You can't use looping sounds (or something along those lines) on buffs... Kind of a bummer when things like that happen...
Oh.. And sometimes, if transformations are done over each other, you can lose control. Thank god, before I fixed that in my map, it was only temporary control loss.